Abstract
After Zika virus (ZIKV) infection in Costa Rica was confirmed in January 2016, the national surveillance system was enhanced to monitor associated birth defects. To characterize the ZIKV outbreak among live-born infants during March 2016–March 2018, we conducted a descriptive analysis. Prevalence of ZIKV-associated birth defects was 15.3 cases/100,000 live births. Among 22 infants with ZIKV-associated birth defects, 11 were designated as confirmed (positive for ZIKV) and 11 were designated as probable cases (negative for ZIKV or not tested, but mother was expsed to ZIKV during pregnancy). A total of 91% had microcephaly (head circumference >2 SDs below mean for age and sex), 64% severe microcephaly (head circumference >3 SDs below mean for age and sex), 95% neurodevelopmental abnormalities, 82% brain anomalies, 41% eye abnormalities, and 9% hearing loss. Monitoring children for >1 year can increase identification of ZIKV-associated abnormalities in addition to microcephaly.